Why does my grease pencil's filled outline turn black in render preview?
okay so I figured out that I needed to change the vertex color to the color of the outline. I just needed to open the materials tab and drag and drop the outline color to the vertex color, then things actually started to look right. Also, another way to do this,(and easier) is to turn on paint mode to material. This will use your material base color to paint instead. 
oh, and one more note to add here, the drawing doesn't change, you have to draw with it to see the difference. It was a little confusing and frustrating because I have to redraw my frames now with this new setting, but I'm glad there's a way to fix this.